Exhaust emission purifier with additive feeder unit and pressurized air introducer unit

ABSTRACT

An exhaust emission purifier includes a purification unit provided in an exhaust system of an engine for purifying exhaust gases. The exhaust emission purifier also includes an additive feeder unit operatively coupled to the exhaust system at a position between the internal combustion engine and the purification unit for providing an additive to the exhaust gases. Furthermore, the exhaust emission purifier includes a pressurized air introducer unit for receiving air pressurized by an air compressor unit, which is driven by the exhaust gases flowing in the exhaust system and compresses intake air flowing in an intake system of the internal combustion engine. The pressurized air introducer unit is operatively coupled to the additive feeder unit for providing the air pressurized by the air compressor unit to the additive feeder unit.

CROSS REFERENCE TO RELATED APPLICATION

The following is based on and claims priority to Japanese PatentApplication No. 2006-167126, filed Jun. 16, 2006, which is herebyincorporated reference in its entirety.

FIELD

The following relates generally to an exhaust emission purifier and,more specifically, to an exhaust emission purifier with an additivefeeder unit and a pressurized air introducer unit.

BACKGROUND

It is known to provide an internal combustion engine such as a dieselengine with a purification unit such as a diesel particulate filter(hereinafter referred to as “DPF”) and a NOx reduction catalyst. Forexample, the purification unit feeds fuel, urea, or the like as anadditive in order to regenerate the purification unit or to trigger acatalytic oxidation-reduction reaction. Examples of this purificationdevice are disclosed in JP-2004-011463A and JP-2004-308526A. Theadditive is ejected into the exhaust gases flowing in the exhaust systemto be delivered to the purification unit. The additive is fed in a finespray form for promotion of the regeneration and the reaction in thepurification unit. For this purpose, the additive is fed usinghigh-pressure air from the additive feeder so that the atomization ofthe additive is promoted.

Typically, larger vehicles such as trucks include a high-pressure airsupply source such as a mechanical compressor which is structuredindependently of the internal combustion engine. However, for smallervehicles such as a passenger car, there may not be enough space toaccommodate the high-pressure air supply source.

In view of the above, there exists a need for an exhaust emissionpurifier with an additive feeder and a pressurized air introducer unitfor an internal combustion engine which overcome the above mentionedproblems in the conventional art. The following addresses this need aswell as other needs as will become apparent to those skilled in the artfrom this disclosure.

SUMMARY

An exhaust emission purifier is disclosed that includes a purificationunit provided in an exhaust system of an internal combustion engine forpurifying exhaust gases flowing in the exhaust system. The exhaustemission purifier also includes an additive feeder unit operativelycoupled to the exhaust system at a position between the internalcombustion engine and the purification unit for providing an additive tothe exhaust gases flowing in the exhaust system. Furthermore, theexhaust emission purifier includes a pressurized air introducer unit forreceiving air pressurized by an air compressor unit, which is driven bythe exhaust gases flowing in the exhaust system and compresses intakeair flowing in an intake system of the internal combustion engine. Thepressurized air introducer unit is operatively coupled to the additivefeeder unit for providing the air pressurized by the air compressor unitto the additive feeder unit.

An additive feeder is disclosed for providing an additive to apurification unit of an exhaust system of an internal combustion engine.The additive feeder included an additive injection valve operativelycoupled to the exhaust system at a position between the internalcombustion engine and the purification unit. The additive injectionvalve injects the additive into exhaust gases flowing in the exhaustsystem. A pressurized air introducer unit is further included forreceiving air pressurized by an air compressor unit, which is driven bythe exhaust gases flowing in the exhaust system and compresses intakeair flowing in an intake system of the internal combustion engine. Thepressurized air introducer unit is operatively coupled to the additiveinjection valve for providing the air pressurized by the air compressorunit to the additive injection valve.

An exhaust purification system is disclosed for an internal combustionengine that includes a purification unit provided in an exhaust systemof an internal combustion engine for purifying exhaust gases flowing inthe exhaust system. The exhaust purification system also includes anadditive feeder unit operatively coupled to the exhaust system at aposition between the internal combustion engine and the purificationunit for providing an additive to the exhaust gases flowing in theexhaust system. Furthermore, an air compressor unit is included with aturbine provided in the exhaust system and driven by the exhaust gasesflowing in the exhaust system. The air compressor unit further includesa compressor provided in an intake system of the internal combustionengine and driven by the turbine. The compressor pressurizes intake airflowing in the intake system. Moreover, the exhaust purification systemincludes a pressurized air introducer unit for receiving air pressurizedby the air compressor unit and is operatively coupled to the additivefeeder unit for providing the air pressurized by the air compressor unitto the additive feeder unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features, and advantages will become more apparent fromthe following detailed description made with reference to theaccompanying drawings, in which like parts are designated by likereference numbers and in which:

FIG. 1 is a schematic diagram illustrating an exhaust purificationsystem according to a first embodiment;

FIG. 2 is a graph showing the relationship between the pressure of airsupplied to an additive injection valve and the drop-diameter of adroplet of the injected additive;

FIG. 3 is a schematic diagram illustrating an exhaust purificationsystem according to a second embodiment;

FIG. 4 is a graph illustrating the relationship between the boostpressure, and the engine rotational speed and output torque;

FIG. 5A is a graph showing the change in the amount of absorption of NOxabsorbed in the NOx reduction catalyst during the engine operationperiod;

FIG. 5B is a graph showing the change in boost pressure during theengine operation period and the change in supply pressure of the airsupplied to the additive injection valve;

FIG. 6 is a schematic diagram illustrating an exhaust purificationsystem according to a third embodiment; and

FIG. 7 is a schematic diagram illustrating an exhaust purificationsystem according to a fourth embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various embodiments according to the present disclosure will bedescribed below with reference to the accompanying drawings. In theseembodiments, structural components that are substantially the same aredesignated by the same reference numerals and repetitive description isomitted.

First Embodiment

FIG. 1 is an exhaust purification system for an internal combustionengine to which an exhaust emission purifier according to a firstembodiment is applied. As illustrated in FIG. 1, the exhaustpurification system 10 of the first embodiment purifies the exhaustgases emitted from a diesel engine 11 (hereinafter referred to as“engine”) serving as an internal combustion engine. The exhaustpurification system 10 is equipped with a purification unit 20, anadditive feeder unit (32), an air compressor unit (e.g., a turbocharger40), and a pressurized air introducer unit 50. The engine 11 includes anexhaust system 60 and an intake system 70.

The exhaust system 60 guides exhaust gases from the engine 11 to an areaoutside of the engine 11. The exhaust system 60 has an exhaust pipe 61that forms an exhaust passage 62. The exhaust gases emitted from theengine 11 flow through the exhaust passage 62 to the outside. Theexhaust passage 62 defined by the exhaust pipe 61 is fluidly coupled tothe engine 11 and an exhaust port 63. The purification unit 20 providedin the exhaust system and is operatively coupled to the exhaust pipe 61.Specifically, the purification unit 20 is disposed between the engine 11and the exhaust port 63 in the exhaust system 60.

The intake system 70 supplies intake air to the engine 11 from an areaoutside the engine 11. The intake system 70 has an intake pipe 71 thatdefines an intake passage 72. The intake air introduced from an intakeport 73 flows through an intake passage 72 into the engine 11. Theintake passage 72 defined by the intake pipe 71 is fluidly coupled tothe intake port 73 and the engine 11. A throttle 74 is disposed in theintake passage 72 for adjusting a flow rate of the intake air.

The purification unit 20 is disposed in the exhaust system 60. In theembodiment shown, the purification unit 20 has a DPE 21, a NOx reductioncatalyst 22 and an oxidation catalyst 23. The DPE 21 collectsparticulate matter (PM) included in the exhaust gases. The NOx reductioncatalyst 22 reduces NOx included in the exhaust gases in cooperationwith, for example, fuel, such as light oil, and urea as the additive. Asa result, the NOx included in the exhaust gases is reduced to N₂, CO₂,and H₂O which are less harmful. The oxidation catalyst 23 oxidizes PMincluded in the exhaust gases. The first embodiment describes an exampleof the purification unit 20 provided with the DPF 21, the NOx reductioncatalyst 22 and the oxidation catalyst 23. However, it will beappreciated that any suitable purification unit 20 may be provided. Forinstance, in one embodiment, the NOx reduction catalyst 22 and eitherthe DPF 21 or the oxidation catalyst 23 is provided. In anotherembodiment, the purification unit 20 is provided with a filter and acatalyst in place of the DPF 21, the NOx reduction catalyst 22, or theoxidation catalyst 23 which are exemplified above.

The additive feeder unit 32 is operatively coupled to the exhaust system60 at a position between the engine 11 and the purification unit 20 forproviding an additive to the exhaust gases flowing in the exhaust system60. In the embodiment shown, the additive feeder unit 32 includes anadditive injection valve 30 that is in fluid communication with theexhaust system 60 between the engine 11 and the purification unit 20. Inother words, the injection valve 30 is closer to the engine 11 than thedistance between the purification unit 20 and the engine 11.

As will be described below, air from the pressurized air introducer unit50 allows the injection valve 30 to feed additive into the exhaustsystem 60. The additive injection valve 30 injects the additive into theexhaust gases flowing in the exhaust passage 62. The additive comprisessubstances performing the functions of the DPF 21, the NOx reductioncatalyst 22 and the oxidation catalyst 23 of the purification unit 20.

For example, the DPF 21 collects the PM included in the exhaust gases.Therefore, when the DPF 21 collects more than a predetermined amount ofPM, the DPF 21 can become clogged, resulting in a reduction in functionof the DPF 21. To avoid this, the additive injection valve 30 injects,for example, fuel such as light oil as the additive, to burn off the PMcollected by the DPF 21. As a result, the clogging of the DPF 21 isreduced, so that the DPF 21 is regenerated.

Also, the NOx reduction catalyst 22 absorbs the NOx included in theexhaust gases. Therefore, when the NOx reduction catalyst 22 absorbsmore than a predetermined amount of NOx, the absorption capacity issaturated, resulting in a reduction in function of the NOx reductioncatalyst 22. To avoid this, the additive injection valve 30 injects, forexample, fuel such as light oil or urea which is an additive serving asa reducer, to thereby reduce the NOx absorbed in the NOx reductioncatalyst 22. As a result, the NOx reduction catalyst 22 is regenerated.

Moreover, the oxidation catalyst 23 burns off the PM included in theexhaust gases. Therefore, fuel is required to burn off the PM. For thispurpose, the additive injection valve 30 injects, for example, fuel suchas light oil as the additive, so that the PM is burned off in theoxidation catalyst 23. As a result, the PM included in the exhaust gasesburns, resulting in a reduction in exhaust emission to the outside.

In this manner, by feeding the additive from the additive injectionvalve 30 to the purification unit 20, the DPF 21, the NOx reductioncatalyst 22 and the oxidation catalyst 23 constituting the purificationunit 20 perform their functions.

The additive injection vale 30 injects light oil which is the fuel forthe engine 11, urea and/or the like as the additive as described aboveinto the exhaust gases flowing in the exhaust passage 62. For thispurpose, the additive injection valve 30 is connected to an additivetank 31 such as a fuel tank. The additive is supplied from the additivetank 31 to the additive injection valve 30.

The turbocharger 40 has a turbine 41 disposed in the exhaust system 60,and a compressor 42 disposed in the intake system 70. The turbine 41 isdisposed in the exhaust passage 62 between the engine 11 and theadditive injection valve 30. In other words, the turbine 41 is closer tothe engine 11 than the distance between the injection valve 30 and theengine 11. The compressor 42 is disposed in the intake passage 72between the intake port 73 and the throttle 74. In other words, thecompressor 42 is closer to the intake port 73 than the distance betweenthe intake port 73 and the throttle 74.

The turbine 41 is rotatably driven by the high-pressure exhaust gasesflowing in the exhaust passage 62. The turbine 41 and the compressor 42are rotatably coupled to each other by a shaft 43. For this reason, whenthe turbine 41 is driven by the flow of the exhaust gases, thecompressor 42 is rotated together with the turbine 41. This allows thecompressor 42 to pressurize and transport the air flowing in the intakepassage 72 toward the engine 11. As a result, the intake air iscompressed and sent to the engine 11.

The pressurized air introducer 50 is fluidly and operatively coupled tothe intake system 70 and the additive injection valve 30. One end of thepressurized air introducer 50 is fluidly coupled to the intake system 70at a position between the engine 11 and the compressor 42. In otherwords, this end of the pressurized air introducer 50 is closer to theengine 11 than the distance between the compressor 42 and the engine 11.The other end of the pressurized air introducer 50 is fluidly coupled tothe additive injection valve 30, which injects the additive into theexhaust passage 62. As such, the compressor 42 pressurizes air in theintake passage 72, the pressurized air introducer 50 receives at least aportion of the air pressurized by the compressor 42, and the pressurizedair introducer 50 delivers the pressurized air to the additive injectionvalve 30. Then, the additive injection valve 30 injects the additiveinto the exhaust system 50 along with the high-pressure air introducedfrom the pressurized air introducer 50. As a result, the additiveejected from the additive injection valve 30 is formed into a fine sprayat least partly due to injection of the high-pressure air introducedfrom the pressurized air introducer 50.

The additive ejected from the additive injection valve 30 has preferablya smaller drop-diameter, in order for the additive to promote theregeneration of and the burning in the purification unit 20 so that thepurification unit 20 can perform its function. As shown in FIG. 2, theadditive ejected from the additive injection valve 30, after forminginto the fine spray, has droplets which become smaller in drop-diameterwith the increase in the pressure of the air injected together with theadditive from the additive injection valve 30. In other words, when theadditive is ejected from the additive injection valve 30, the ejectionof the additive along with the high-pressure air decreases thedrop-diameter of the droplets of the ejected additive. As a result, theregeneration of and the burning in the purification unit 20 is promotedto enable the purification unit 20 to perform its function moreeffectively.

In this manner, in the first embodiment, highly pressurized air isintroduced to the additive injection valve 30 from a position betweenthe compressor 42 of the turbocharger 40. Thereby, when the additive isejected from the additive injection valve 30, the high-pressure air isejected along with the additive. This decreases the drop-diameter of thedroplets of the additive ejected from the additive injection valve 30 topromote the formation into a fine spray and the reduction indrop-diameter of the additive. As a consequence, it is possible to exertthe function of the purification unit 20 with high effectiveness andprecision, and therefore to reduce the substances, such as PM and NOx,included in the exhaust gases.

Furthermore, in the case of the engine 11 equipped with the turbocharger40, the high-pressure air can be provided to the injection valve 30 evenwithout an additional high-pressure air supply source, such as amechanical compressor, for example. Thus, a large sized high-pressureair supply source is not required, resulting in reduction of the spatialconstraints of the system.

Second Embodiment

FIG. 3 illustrates an exhaust purification system according to a secondembodiment. In the second embodiment shown in FIG. 3, the pressurizedair introducer 50 of the exhaust purification system 10 has a checkvalve 51. In the embodiment shown, the check valve 51 is disposed at theend of the pressurized air introducer 50 adjacent to the intake system70. The check valve 51 permits the flow of air through the pressurizedair introducer 50 from the intake passage 72 to the additive injectionvalve 30. Also, the check valve 51 blocks the flow of air through thepressurized air introducer 50 from the additive injection valve 30generally toward the intake passage 72. That is, the check valve 51opens when the pressure in the intake passage 72 exceeds the pressure inthe pressurized air introducer 50 adjacent the additive injection valve30 and closes when the pressure in the intake passage 72 is lower thanthe pressure in the pressurized air introducer 50 adjacent the additiveinjection valve 30. By providing the check valve 51, the most highlypressurized air produced in the intake passage 72 is stored in thepressurized air introducer 50 from a point when the check valve 51closes to a point when the additive injection valve 30 injects theadditive. The check valve 51 is preferably disposed closer to aboost-pressure inlet port of the piping connecting between the additiveinjection valve 30 and the intake passage 72. In other words, the checkvalve 51 is provided in a position as close as possible to the intakepassage 72, so as to increase the volume for storing the high-pressureair as much as possible.

As illustrated in FIG. 4, the boost pressure produced by theturbocharger 40 is varied by the rotational speed and the output torqueof the engine 11. Specifically, the higher the rotational speed of theengine 11 and the greater the output torque, the higher the boostpressure produced by the turbocharger 40. However, the operationconditions of the engine 11, that is, the rotational speed and theoutput torque, vary every moment. Because of this, as shown in FIG. 5B,the boost pressure also varies every moment in accordance with theoperation conditions of the engine 11.

On the other hand, for example, the regeneration of the NOx reductioncatalyst 22 is started at the time when the amount of stored NOx, whichincreases with increased operation time of the engine 11, reaches apredetermined upper limit value M as shown in FIG. 5A. At this point, ifthe boost pressure is reduced by the operation conditions of the engine11 as shown by the broken line in FIG. 5B, the pressure of the air whichis to be ejected together with the additive from the additive injectionvalve 30 may be possibly reduced.

To avoid this, the check valve 51 is provided. As a result, even whenthe boost pressure varies as shown by the broken line in FIG. 5B, thepressure in the pressurized air introducer 50, that is, the pressuresupplied to the additive injection valve 30, is at the maximum value ofthe boost pressure as shown by the solid line in FIG. 5B. In otherwords, the maximum boost pressure which is produced from the time of thelast injection of the additive to the time of the current injection ofthe additive is maintained as the supply pressure of the pressurized airin the pressurized air introducer 50. For this reason, when theregeneration of the NOx reduction catalyst 22 is required, even if a lowboost pressure is produced by the turbocharger 40 in accordance with theoperation conditions of the engine 11, the air maintained at thehigh-pressure in the pressurized air introducer 50 promotes the sprayformation of the additive ejected from the additive injection valve 30.

In the second embodiment, by providing the check valve 51, the pressureof the air supplied from the pressurized air introducer 50 to theadditive injection valve 30 is maintained at the maximum value producedin the intake passage 72 until the injection of the additive. This makespossible the constant supply of the high-pressure air to the additiveinjection valve 30 irrespective of the operation conditions of theengine 11, thus promoting the spray formation of the additive injected.

The check valve 51 may be placed in any position in the pressurized airbetween the intake passage 72 and the additive injection valve 30.However, if the check valve 51 is disposed at the end of the pressurizeair introducer 50 adjoining the intake passage 72, the volume of thepressurized air introducer 50 is increased, thus increasing the capacityof the high-pressure air. In addition, the second embodiment hasdescribed the case when the NOx reduction catalyst 22 is regenerated, asan example, but likewise, the DPF 21 is regenerated when the amount ofPM collected reaches a predetermined amount.

Third Embodiment

FIG. 6 illustrates an exhaust purification system according to a thirdembodiment. In the case of the third embodiment shown in FIG. 6, thepressurized air introducer 50 of the purification system 10 includes areservoir 52. The reservoir 52 is disposed between the intake system 70and the additive injection valve 30. More specifically, the reservoir 52is disposed between the check valve 51 and the additive injection valve30. The reservoir 52 has a greater axial cross sectional area than theother portions of the pressurized air introducer 50. Thus, the reservoir52 is an air capacity portion for storing the air introduced into thepressurized air introducer 50. That is, the reservoir 52 stores thehigh-pressure air introduced into the pressurized air introducer 50.

When the high-pressure air is ejected along with the additive from theadditive injection valve 30 for exerting the function of thepurification unit 20, it is preferable that the high-pressure air issupplied continuously in accordance with the additive injection period.For this purpose, in the third embodiment, the reservoir 52 is providedfor increasing the volume of the pressurized air introducer 50. Thus,the high-pressure air introduced from the intake passage 72 is stored inthe reservoir 52 in addition to the pressurized air introducer 50. As aconsequence, in the third embodiment, the high-pressure air stored inthe reservoir 52 is supplied when the additive is ejected, to therebycontinuously promote the atomization of the additive irrespective of theoperation conditions of the engine 11.

Fourth Embodiment

FIG. 7 illustrates an exhaust purification system according to a fourthembodiment.

In the case of the fourth embodiment shown in FIG. 7, the pressurizedair introducer 50 of the exhaust purification system 10 has a flow-ratecontrol unit 53. The flow-rate control unit 53 blocks flow from theintake system 70 to the additive injection valve 30 when the rate offlow in the pressurized air introducer 50 exceeds a predetermined value.In other words, the flow-rate control unit 53 blocks introduction of thehigh-pressure air into the pressurized air introducer 50 when the flowrate of air supplied from the intake passage 72 to the pressurized airintroducer 50 exceeds a predetermined value. Thus, the flow-rate controlunit 53 is a flow limiter for controlling the flow rate of intake airfrom the intake passage 72 to the pressurized air introducer 50.

For example, if the pressurized air introducer 50 is damaged and an airleak occurs in the pressurized air introducer 50, the air introducedfrom the intake passage 72 is emitted from the pressurized airintroducer 50 to the outside. For this reason, the intake airpressurized by the turbocharger 40 is not supplied to the engine 11,resulting in a reduction in boost pressure of the turbocharger 40. As aresult, the engine 11 is unlikely to achieve a predetermined output.

To avoid this condition, in the fourth embodiment, when the flow rate ofintake air introduced from the intake passage 72 to the pressurized airintroducer 50 becomes excessively high, the air introduction is blocked.Thus, a reduction in boost pressure produced by the turbocharger 40 isless likely and the output of the engine 11 can be stably sustained.

While only the selected example embodiments have been chosen toillustrate the present disclosure, it will be apparent to those skilledin the art from this disclosure that various changes and modificationscan be made therein without departing from the scope of the disclosureas defined in the appended claims. Furthermore, the foregoingdescription of the example embodiments according to the presentdisclosure is provided for illustration only, and not for the purpose oflimiting the disclosure as defined by the appended claims and theirequivalents.

1. An exhaust emission purifier, comprising: a purification unitprovided in an exhaust system of an internal combustion engine forpurifying exhaust gases flowing in the exhaust system; an additivefeeder unit operatively coupled to the exhaust system at a positionbetween the internal combustion engine and the purification unit forproviding an additive to the exhaust gases flowing in the exhaustsystem; and a pressurized air introducer unit for receiving airpressurized by an air compressor unit, which is driven by the exhaustgases flowing in the exhaust system and compresses intake air flowing inan intake system of the internal combustion engine, wherein thepressurized air introducer unit is operatively coupled to the additivefeeder unit for providing the air pressurized by the air compressor unitto the additive feeder unit.
 2. An exhaust emission purifier accordingto claim 1, further comprising a check valve that permits flow throughthe pressurized air introducer unit from the intake system and blocksflow through the pressurized air introducer unit from the additivefeeder unit generally toward the intake system.
 3. An exhaust emissionpurifier according to claim 1, wherein the pressurized air introducerunit includes a reservoir provided between the intake system and theadditive feeder unit for storing the air pressurized by the aircompressor unit.
 4. An exhaust emission purifier according to claim 1,wherein the pressurized air introducer unit includes a flow-rate controlunit that blocks flow from the intake system to the additive feeder unitwhen a rate of flow in the pressurized air introducer unit exceeds apredetermined value.
 5. An exhaust emission purifier according to claim1, wherein the air compressor unit is a turbocharger.
 6. An additivefeeder for providing an additive to a purification unit of an exhaustsystem of an internal combustion engine, the additive feeder comprising:an additive injection valve operatively coupled to the exhaust system ata position between the internal combustion engine and the purificationunit, wherein the additive injection valve injects the additive intoexhaust gases flowing in the exhaust system; and a pressurized airintroducer unit for receiving air pressurized by an air compressor unit,which is driven by the exhaust gases flowing in the exhaust system andcompresses intake air flowing in an intake system of the internalcombustion engine, wherein the pressurized air introducer unit isoperatively coupled to the additive injection valve for providing theair pressurized by the air compressor unit to the additive injectionvalve.
 7. An additive feeder according to claim 6, further comprising acheck valve that permits flow through the pressurized air introducerunit from the intake system and blocks flow through the pressurized airintroducer unit from the additive feeder valve generally toward theintake system.
 8. An additive feeder according to claim 6, wherein thepressurized air introducer unit includes a reservoir provided betweenthe intake system and the additive injection valve for storing the airpressurized by the air compressor unit.
 9. An additive feeder accordingto claim 6, wherein the pressurized air introducer unit includes aflow-rate control unit that blocks flow from the intake system to theadditive injection valve when a rate of flow in the pressurized airintroducer unit exceeds a predetermined value.
 10. An additive feederaccording to claim 6, wherein the air compressor unit is a turbocharger.11. An exhaust purification system for an internal combustion engine,comprising: a purification unit provided in an exhaust system of aninternal combustion engine for purifying exhaust gases flowing in theexhaust system; an additive feeder unit operatively coupled to theexhaust system at a position between the internal combustion engine andthe purification unit for providing an additive to the exhaust gasesflowing in the exhaust system; an air compressor unit that includes aturbine provided in the exhaust system and driven by the exhaust gasesflowing in the exhaust system, the air compressor unit further includinga compressor provided in an intake system of the internal combustionengine and driven by the turbine, wherein the compressor pressurizesintake air flowing in the intake system; and a pressurized airintroducer unit for receiving air pressurized by the air compressor unitand is operatively coupled to the additive feeder unit for providing theair pressurized by the air compressor unit to the additive feeder unit.12. An exhaust purification system for an internal combustion engineaccording to claim 11, further comprising a check valve that permitsflow through the pressurized air introducer unit from the intake systemand blocks flow through the pressurized air introducer unit from theadditive feeder unit generally toward the intake system.
 13. An exhaustpurification system for an internal combustion engine according to claim11, wherein the pressurized air introducer unit includes a reservoirprovided between the intake system and the additive feeder unit forstoring the air pressurized by the air compressor unit.
 14. An exhaustpurification system for an internal combustion engine according to claim11, wherein the pressurized air introducer unit includes a flow-ratecontrol unit that blocks flow from the intake system to the additivefeeder unit when a rate of flow in the pressurized air introducer unitexceeds a predetermined value.
 15. An exhaust purification systemaccording to claim 11, wherein the air compressor unit is aturbocharger.